The present invention relates to a transmission ultrasonic microscope which radiates ultrasonic waves into an object to be measured and which detects changes in the velocity of the ultrasonic waves propagating in the object by a focusing ultrasonic receiving element in accordance with interferometry principles.
The present inventor has previously proposed an improvement over a conventional ultrasonic microscope of confocal assembled type which uses focusing concave transducers at the radiating and detecting sides. According to the proposed ultrasonic microscope, a plane ultrasonic transducer is used at the radiating side and a focusing concave ultrasonic transducer is used at the detecting side.
However, in this proposed ultrasonic microscope, since the radiating area of the plane ultrasonic transducer is wide, the required electric power increases. Furthermore, radiation of ideal plane waves is not easy, and the sound field tends to become nonuniform due to diffraction. Adjustment of the tilt angle of the plane ultrasonic transducer is time-consuming, and interference tends to be caused between a flat sample and the plane ultrasonic transmitter.